code: def test_batches_per_epoch():
      loader = MultiProcessDataLoader(
          MockDatasetReader(),
          "some path",
          batch_size=4,
          batches_per_epoch=10,
      )
      vocab = Vocabulary.from_instances(loader.iter_instances())
      loader.index_with(vocab)
  
      assert len(loader) == 10
      assert len(list(loader)) == 10
  
imports: from typing import List, Iterable, Dict
  import torch
  import pytest
  from allennlp.common.testing import requires_gpu
  from allennlp.data.instance import Instance
  from allennlp.data.dataset_readers import DatasetReader
  from allennlp.data.data_loaders import MultiProcessDataLoader, WorkerError
  from allennlp.data.fields import Field, TextField, MetadataField, TensorField
  from allennlp.data.tokenizers import PretrainedTransformerTokenizer
  from allennlp.data.token_indexers import PretrainedTransformerIndexer
  from allennlp.data.vocabulary import Vocabulary
  from allennlp.data.data_loaders.data_collator import LanguageModelingDataCollator
label_desc: Use image node_id 5 for calling a global function with example usage: test_batches_per_epoch() without return types